As the title says, this is pretty minor....
The wording for handling the If-Modified-Since header uses a MUST when
describing when to send back a 304 response. My understanding of
MUST/SHOULD/MAY is that MUST is to be used for requirements neccessary for
interoperability or correct functioning of the protocol. Since the sending
of a 304 response doesn't impact interoperability or correctness (the
protocol is unharmed but less efficient if a server ignores I-M-S and always
sends back the data), this should probably be a SHOULD.
(And no, IIS doesn't ignore I-M-S. This was brought up to me by a
non-Microsoft person writing an ISAPI app).
Henry